I bought a used 5th gen iPod touch last week for my girlfriend's sister, and I figured I'd play around with it by installing iOS 7, and downgrade to iOS 6 when I eventually give it to her. I did a DFU restore to 6.1.3, and the restore completed fine. However, when I plugged it into iTunes, it said that the iPod was already activated with an Apple ID, and that I'd have to log in using that Apple ID. It was my Apple ID, so I figured it would be no problem. When I typed in my password, the form just reset itself. I tried a couple more times, and still no luck. I thought I'd have to call Apple support to help me out, which is one thing I didn't ever expect to do, as I knew what I was getting myself into when installing the beta. The solution was to go through the setup process on the iPod (or iPhone) itself. Once you log in to the associated Apple ID on the device, you can complete the process in iTunes without issues.